Bad news for Mary-Kate Olsen at a big equestrian show in NY this week -- when her horse refused to jump during one of the events ... leaving her with a big fat zero on the score sheet.
It all went down at the 39th Annual Hampton Classic Horse Show -- where the 28-year-old former "Full House" actress was attempting to show off her talents in the saddle.
But according to multiple reports, her brown horse (named Uniek) wasn't in the jumping mood -- and ruined the run.
Don't worry ... MKO got on another horse (named Swagger) who seemed more up for the challenge.
As for Olsen's twin sister -- she has yet to be seen at the event.
Luckily she didn't fall off the horse and get amnesia this time.